We are exposed daily to several industrial chemicals in low levels. These same chemicals cross the placenta barrier and affect thyroid function in developing babies.
Why is this important? In pregnancy, thyroid hormones are responsible for fetal brain development and low level exposures to certain chemicals affect cognitive development in developing babies. There is an enzyme called CYP1A1 in the liver that transforms endocrine-disrupting chemicals into a different form that interferes with thyroid hormone receptors. Researchers looked at this enzyme in placental tissue and they got a clear view of thyroid function being interfered with on a cellular level by environmental chemicals.
I have reversed hundreds of thyroid disorders using environmental medicine. I specialize in reversing disease on a cellular level. We run full thyroid and environmental panels to individualize your protocol.
Smokers during pregnancy had higher levels of CYP1A1 in placental tissue. Cigarettes contain 5000 chemicals that disrupt the endocrine system and cause cancers.
Double whammy - if you smoke and you are exposed to higher levels of dioxin compounds then the body activates these chemicals and your thyroid function will be altered. Chemicals can interfere with your thyroid hormone function and may not be revealed by changes in your serum thyroid hormone levels. 
